Vonleh is definately my #1 pick.
He's got the mobility and outside shooting touch to play PF, and the length, strength, toughness, post game.and shotblocking ability to play center. Hes got the elite reboumding skills for either position.
I think he's a very low risk player. Hes got a his attitude so there's little risk of him becoming a demarcus cousins attitude guy. If his low post game struggles against NBA size then hes got q silky smooth jumper (out to three point range) as a backup, and hes also skilled at gettimg to the line (where he shoots a nice percentage).
His versatile offensive game combined with his great rebounding means he'll most likely be a double-double guy in the nba, and given his age (18) the sky is the limit.
Second choose is Smart, because after Parker he's probably the next best scorer in the top 10, and Boston could use that extra offensive spark.